I have been running a Trident on my 75G system for at least a yr now and have been pretty happy with it. Just installed a second one on my new 200G system. I had been doing manual tests with Hanna checker while it's just fish and have been in the 8-8.3 range (dosing 2 part). My plan is once the new tank is stable I'd start transferring some of the corals from my 75 to the 200. I set up the second trident a couple days ago and it was reading in the 7.6-7.8 range. Wasn't too concerned since it's been sitting in the basement since August in the box and you're supposed to let it run a couple days before calibrating it. Ran a calibration today and everything checked out, next test Alk was back at 7.5. Double checked with the Hanna, it was reading 8.2. Hmmmmmm, so I did a check on my 75 with the Hanna. That trident (separate unit) was showing 8.7, Hanna says 9.3. Hmmmmmmm again. So I used the Salifert on the 75 to see which was "right" and got 9.2. Wierd. So either I have 2 tridents reading off, my Hanna and Salifert are both off, or I'm crazy. I'm not really chasing any particular parameter, just want stability, but to me there is a difference between 7.5 and 8.2 as the baseline. Just wondered if anyone had any ideas or seen anything similar? I started to poke around on the Neptune Systems support page, but that user forum is a mess. Looks like most questions/requests don't get any answers. Thanks for any insights.